From:	Charles Sandmann <sandmann AT new-orleans DOT NeoSoft DOT com>
Subject:	Re: Interrupt Handler / Page Faults
To:	norvax!norvax!leroy AT uunet DOT uu DOT net (Todd LeRoy)
Date:	Wed, 8 Feb 1995 07:56:18 -0600 (CST)
Cc:	djgpp AT sun DOT soe DOT clarkson DOT edu (DJGPP Mailing List)

> If I am understanding you correctly, [lack of page locking support in GO32]
> means that it is impossible for
> me to write a program which does something like serial communications (i.e.
> has an ISR) which will run reliably under DJGPP.  Is this true???  If it
> is, it could have serious implications for our intended use.

Well, not impossible, just inconvenient for a few months.

If your application has enough memory to run without page faulting, it will run
fine under GO32 with the right setup.  You disable virtual memory by setting
the GO32TMP environment variable to point to a non existent disk.  To
be completely sure it will work, read the memory the ISR touches before
hooking the interrupt.

If your application calls DPMI services to lock those pages into memory
you should not have any problems.  This is the recommended solution,
since it will work with V2, and with V1 under DPMI providers.  A free DPMI
provider which robustly handles HW interrupts is now finished and will
be available real-soon (so you will be able to do this under V1 using 
the CWSDPMI to provide DPMI services).

So, the solutions to this problem already exist, it is just a matter of
getting it put together.  I hope this also helps explain another 
reason why V2 is DPMI only - not just to irritate developers!

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